Computer Controlled Rotational Molding of a Hollow Femur for 3-D Photoelastic Analysis

Abstract

The rotational molding technique was utilized in the fabrication of hollow femur models for the expressed purpose of photostress analysis. Advances in computer control coupled with the development of proper experimental protocols enabled the consistent and automated reproduction of the joint model. Such considerations proved to be critical in overcoming the limitations of prevailing rotational molding operations. The use of hollow rotation molded models was advantageous as it better represented the physiologic constitution of real bones, thereby, conferring a greater degree of accuracy in the photostress experiments. The fabrication of the hollow models entailed flow visualization studies, which assessed the variation in rotational speeds with time as well as the optimum relative rotation speeds to be adopted. The preferred mode of rotational motion was also determined through a series of simulated experiments to determine whether steady or repetitive cyclical rotational modes were more beneficial. The fabricated hip models were loaded and the stress profiles examined. Contour maps of the stress fringes manifested in the photoelastic analysis indicated several sites of stress concentrations. These sites coincided with physiologic patterns of hip fractures, verifying the validity of the hollow femoral models. Computer controlled rotational molding has proven to be a feasible manufacturing process in the development of hollow physiologically representative femur models.